This invention concerns extreme-pressure (EP) lubricating oil.
High-load conditions often occur in the gear sets used in automotive transmission differentials, pneumatic tools, gas compressors, high-pressure hydraulic systems, metal-working and similar devices as well as in many types of bearings. In order to avoid the undesirable effects which result when using an uncompounded oil under these high-load conditions, the lubricants for use in such service contain EP agents. For the most part, EP agents have been organic or metallo-organic compounds which are oil soluble or easily incorporated as a stable dispersion in the oil.
Recently, Peeler in U.S. Pat. No. 3,313,727 disclosed an EP lubricant produced by the dispersion in a nonpolar lubricating oil of an inorganic hydrated sodium or potassium borate. To prepare the lubricant, the borate, water and an emulsifier were introduced into the nonpolar medium. The mixture was then agitated to produce a microemulsion of the aqueous borate solution in the oil and thereafter heated to remove the liquid water. Peeler also disclosed that conventional additives such as rust inhibitors, foam inhibitors, etc., could be present in the finished lubricating composition containing the borate.
The borate-containing oils described by Peeler have, however, a very serious deficiency in service. If water is introduced into the system containing the borate lubricant, the borate crystallizes out of the oil and forms hard granules. These granules can cause severe noise in the system and in some cases damage the gears or bearings themselves. Further, loss of the borate by crystallization substantially decreases the EP function of the lubricant.
Although the borate dispersion prepared by Peeler has excellent extreme-pressure properties, it has been found that in sealed systems dispersions with high water content have an adverse effect on the seals. It is believed that the alkali metal borate dispersions slowly form solid deposits on shafts at or near the seals. The turning motion of the shafts then slowly abrades the seals, thereby allowing loss of lubricant. In addition, the borate dispersion described by Peeler exhibits a compatibility problem with conventional lubricating oil additives such as phenates, sulfurized fats and zinc dithiophosphate.
It is therefore an object of this invention to provide an extreme-pressure lubricant having improved antiwear properties and which is compatible with lubricating oil additives.